我收到Android应用程序崩溃问题。实际上我试图在Android应用程序的sharedPreference中存储json返回值。哪个没有错误，但应用程序仍在继续崩溃，我尝试多次卸载应用程序并且没有进展。我不知道错误，再次我是新的共享首选项，实际上这个应用程序在我更改之前使用了sqllite。 我试图在sharedpreferance中存储json返回数据，这是我的loginActivity文件：
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import com.android.volley.Request.Method;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.HashMap;
import java.util.Map;
import info.androidhive.loginandregistration.R;
import info.androidhive.loginandregistration.app.AppConfig;
import info.androidhive.loginandregistration.app.AppController;
import info.androidhive.loginandregistration.helper.SQLiteHandler;
import info.androidhive.loginandregistration.helper.SessionManager;
public class LoginActivity extends Activity {
private static final String TAG = RegisterActivity.class.getSimpleName();
private Button btnLogin;
private Button btnLinkToRegister;
private EditText inputEmail;
private EditText inputPassword;
private ProgressDialog pDialog;
private SessionManager session;
private SQLiteHandler db;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
inputEmail = (EditText) findViewById(R.id.email);
inputPassword = (EditText) findViewById(R.id.password);
btnLogin = (Button) findViewById(R.id.btnLogin);
btnLinkToRegister = (Button) findViewById(R.id.btnLinkToRegisterScreen);
// Progress dialog
pDialog = new ProgressDialog(this);
pDialog.setCancelable(false);
// SQLite database handler
db = new SQLiteHandler(getApplicationContext());
// Session manager
session = new SessionManager(getApplicationContext());
// Check if user is already logged in or not
if (session.isLoggedIn()) {
// User is already logged in. Take him to main activity
Intent intent = new Intent(LoginActivity.this, MainActivity.class);
startActivity(intent);
finish();
}
// Login button Click Event
btnLogin.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
String email = inputEmail.getText().toString().trim();
String password = inputPassword.getText().toString().trim();
// Check for empty data in the form
if (!email.isEmpty() && !password.isEmpty()) {
// login user
checkLogin(email, password);
} else {
// Prompt user to enter credentials
Toast.makeText(getApplicationContext(),
"Please enter the credentials!", Toast.LENGTH_LONG)
.show();
}
}
});
// Link to Register Screen
btnLinkToRegister.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
Intent i = new Intent(getApplicationContext(),
RegisterActivity.class);
startActivity(i);
finish();
}
});
}
/**
* function to verify login details in mysql db
* */
private void checkLogin(final String email, final String password) {
// Tag used to cancel the request
String tag_string_req = "req_login";
pDialog.setMessage("Logging in ...");
showDialog();
StringRequest strReq = new StringRequest(Method.POST,
AppConfig.URL_LOGIN, new Response.Listener<String>() {
@Override
public void onResponse(String response) {
Log.d(TAG, "Login Response: " + response.toString());
hideDialog();
try {
JSONObject jObj = new JSONObject(response);
boolean error = jObj.getBoolean("error");
// Check for error node in json
if (!error) {
// user successfully logged in
// Create login session
session.checkLogin();
// Now store the user in SQLite
String uid = jObj.getString("uid");
JSONObject user = jObj.getJSONObject("user");
int id = user.getInt("id");
String name = user.getString("name");
String email = user.getString("email");
String status = user.getString("status");
session.createLoginSession(email,password,id);
Intent intent = new Intent(LoginActivity.this,
MainActivity.class);
intent.putExtra("status",status);
startActivity(intent);
finish();
} else {
// Error in login. Get the error message
String errorMsg = jObj.getString("error_msg");
Toast.makeText(getApplicationContext(),
errorMsg, Toast.LENGTH_LONG).show();
}
} catch (JSONException e) {
// JSON error
e.printStackTrace();
Toast.makeText(getApplicationContext(), "Json error: " + e.getMessage(), Toast.LENGTH_LONG).show();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.e(TAG, "Login Error: " + error.getMessage());
Toast.makeText(getApplicationContext(),
error.getMessage(), Toast.LENGTH_LONG).show();
hideDialog();
}
}) {
@Override
protected Map<String, String> getParams() {
// Posting parameters to login url
Map<String, String> params = new HashMap<String, String>();
params.put("email", email);
params.put("password", password);
return params;
}
};
// Adding request to request queue
AppController.getInstance().addToRequestQueue(strReq, tag_string_req);
}
private void showDialog() {
if (!pDialog.isShowing())
pDialog.show();
}
private void hideDialog() {
if (pDialog.isShowing())
pDialog.dismiss();
}
}
SessionManager 是：
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.util.Log;
import java.util.HashMap;
import info.androidhive.loginandregistration.activity.LoginActivity;
public class SessionManager {
// LogCat tag
private static String TAG = SessionManager.class.getSimpleName();
// Shared Preferences
SharedPreferences pref;
Editor editor;
Context _context;
// Shared pref mode
int PRIVATE_MODE = 1;
// Shared preferences file name
private static final String PREF_NAME = "OnlineShop";
private static final String KEY_IS_LOGGED_IN = "isLoggedIn";
// Email address (make variable public to access from outside)
public static final String KEY_EMAIL = "email";
// Password (make variable public to access from outside)
public static final String KEY_PASS = "password";
//ID userid for the session
public static final String KEY_ID="uid";
public SessionManager(Context context) {
this._context = context;
pref = _context.getSharedPreferences(PREF_NAME, PRIVATE_MODE);
editor = pref.edit();
}
/**
* Create login session
* */
public void createLoginSession(String email, String password, int uid){
// Storing login value as TRUE
editor.putBoolean(KEY_IS_LOGGED_IN, true);
// Storing email in pref
editor.putString(KEY_EMAIL, email);
// Storing password in pref
editor.putString(KEY_PASS, password);
//Storing userid uid in pref
editor.putInt(KEY_ID, uid);
// commit changes
editor.commit();
}
/* public void setLogin(boolean isLoggedIn) {
editor.putBoolean(KEY_IS_LOGGED_IN, isLoggedIn);
editor.commit();
Log.d(TAG, "User login session modified!");
}
*/
/**
* Check login method wil check user login status
* If false it will redirect user to login page
* Else won't do anything
* */
public void checkLogin(){
// Check login status
if(!this.isLoggedIn()){
// user is not logged in redirect him to Login Activity
Intent i = new Intent(_context, LoginActivity.class);
// Closing all the Activities
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
// Add new Flag to start new Activity
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
// Staring Login Activity
_context.startActivity(i);
}
}
/**
* Get stored session data
* */
public HashMap<String, String> getUserDetails(){
HashMap<String, String> user = new HashMap<String, String>();
// user email
user.put(KEY_EMAIL, pref.getString(KEY_EMAIL, null));
// user password
user.put(KEY_PASS, pref.getString(KEY_PASS, null));
//user id
user.put(KEY_ID, pref.getString(KEY_ID, null));
// return user
return user;
}
/**
* Clear session details
* */
public void logoutUser(){
// Clearing all data from Shared Preferences
editor.clear();
editor.commit();
// After logout redirect user to Loing Activity
Intent i = new Intent(_context, LoginActivity.class);
// Closing all the Activities
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
// Add new Flag to start new Activity
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
// Staring Login Activity
_context.startActivity(i);
}
public boolean isLoggedIn(){
return pref.getBoolean(KEY_IS_LOGGED_IN, true);
}
}
错误
03-07 19:26:27.643 1795-1795/? E/AndroidRuntime: FATAL EXCEPTION: main Process:
info.androidhive.loginandregistration,
PID: 1795 java.lang.RuntimeException:
Unable to start activity ComponentInfo{info.androidhive.loginandregistration/info.androidhive.loginandregistration.activity.MainActivity}:
java.lang.NullPointerException: Attempt to invoke virtual method
'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference
答案 0 :(得分：0)
这与在SharedPreferences中存储JSON值无关。崩溃发生的原因不同。在您的MainActivity中，您正在尝试读取Bundle的内容，特别是“status”的值，但问题是您在调用MainActivity时并不总是会添加额外的值，并且很可能您不检查在尝试阅读它之前是否为null。在一个地方你可以调用它：
Intent intent = new Intent(LoginActivity.this, MainActivity.class);
startActivity(intent);
和另一个：
Intent intent = new Intent(LoginActivity.this, MainActivity.class);
intent.putExtra("status",status);
startActivity(intent);
因此，在MainActivity中实现一些正确的错误处理，你应该摆脱这种崩溃。
答案 1 :(得分：0)
public class SharedPreference {
private SharedPreferences mPrefs;
private Context mContext;
private String KEY = "KEY";
private String JSONKEY = "JSONKEY";
public SharedPreference(Context mContext) {
this.mContext = mContext;
mPrefs = PreferenceManager.getDefaultSharedPreferences(mContext);
}
// for saving list in JSON format
public boolean setList(List<String> list)
{
SharedPreferences.Editor prefsEditor = mPrefs.edit();
Gson gson = new Gson();
String json = gson.toJson(list);
prefsEditor.putString(KEY, json);
return prefsEditor.commit();
}
// get list from json format
public List<String> getList()
{
Gson gson = new Gson();
String json = mPrefs.getString(KEY, "");
Type type = new TypeToken<ArrayList<String>>() {}.getType();
return gson.fromJson(json,type);
}
// Set Json
public boolean setJson(JSONObject json)
{
SharedPreferences.Editor prefsEditor = mPrefs.edit();
String jsonString = json.toString();
prefsEditor.putString(JSONKEY, jsonString);
return prefsEditor.commit();
}
// get json
public JSONObject getJson() throws JSONException {
Gson gson = new Gson();
String json = mPrefs.getString(JSONKEY, "");
return new JSONObject(json);
}
}
你应该得到如下的字符串，以避免空指针异常
// string can be null
String status = getIntent().getStringExtra("status");
if(status!= null)
{
// do your work here
}